Electric motors are increasingly being used to drive vehicles, which draw their energy from internal combustion engine driven generators, batteries, or fuel cells. To achieve a higher spread, in many cases shiftable gear stages are arranged after the electric motors, but usually the power transfer is realized without shifting stages. The term “spread” is understood to be the speed range over which nominal power can be reached at the power take off.
For road and rail vehicles, the state-of-the-art procedure currently described usually has been sufficient for achieving the desired driving power. Here, the spread lies on the order of 5-10. The lowest speed at which nominal power is achieved frequently lies over 20 km/h. For agricultural utility vehicles and especially for tractors, this spread is not sufficient. Values over 15 are necessary to cover the driving tasks of a tractor. The lowest speed at which nominal power is achieved lies in the vicinity of 3 km/h. Due to the low absolute speed and high traction force of tractors, shifting processes, with which it must be shifted into a different speed range for a similar traction force, are very uncomfortable due to the transmission jump in the drive system. The continuously variable power shift gears frequently used in tractors typically have two branches, by means of which the torque of the drive module or the energy source is selectively transmitted to the traction drive. When shifting to a different speed range, torque is also transmitted from the drive module to the traction drive during the shifting process (power shift gear). If a shifting process is performed, one branch of the gear is separated or decoupled from the traction drive, while the other branch of the gear is coupled and thus connected to the traction drive. A shifting process is subject to constraining conditions, because the rotational speeds of the two branches must essentially match at the time of the shifting process.
Moreover, in contrast to road and rail vehicles, tractors, in addition to the traction drive, are usually equipped with one or more additional mechanical power take off devices for attachments, a so called power take off (PTO).